Method of manufacturing cathode-ray tube screen structures



July 24, 1956 G. F. BARNETT 2 756,157

METHOD 0E MANUFACTURING cATHoDE-RAY TUBE SCREEN STRUCTURES Filed July 1 0, 1953 H57. Z. F7 Q,

United States Patent O METHOD F MANUFACTURING CATHODE-RA TUBE SCREEN STRUCTURES Guy F. Barnett, Roslyn, Pa., assigner to Philco Corporation, Philadelphia, Pa., a kcorporation of Pennsylvania The invention relates to an improved method of manufactoring cathode ray tube screen structures and also to an improved composition foruse in the practice of the method. In particular, the invention relates to an improved method of depositing certain layers of amultilayer screen structure.

While not limited thereto, the invention is particularly applicable to the manufacture of screen structures for cathode ray tubes for use in reproducing color television images. Accordingly, the invention will be described in detail with reference to its use in color television reproduction.

In certain presently proposed systems of color television, there is transmitted and subsequently received a signal which is representative, at time-spaced intervals, of intelligence concerning ther different primary color components of successively scanned portions of a televised scene. lt has been recognized that an imageof this scene can b'e-reproduced if the received signal is applied to a cathode ray tube and isthere utilized to control the intensity of the electron beam at the same time that` the beam is deiiected across screen elements, each one-of which is emissive of light of one of the aforementioned dili'erent primary colors. In such a receiver `system it is of paramount importance to insure coincidence between the intervals during which the beam intensity is representative of intelligence concerning a particular color and the intervals during which the beam is impingent upon, a screen element emissive of light of that same primary color. A scheme which has proven successful in maintaining such coincidence involvesy the production of electrical signals indicative of beam impingement upon certain screen portions, called indexing elements, which are located in known geometrical relation to the light emissive screen elements. These Lsame signals are then utilized to control either the rate ofz scan of the beam across the screenelements, orthe rate of application of intelligence representative signal portions to the beam intensity control grid of the cathode ray tube, or both.

It has been recognized that a particularly advantageous form which such a screen structure mayvtake comprises a substrate made of a transparent dielectric material, such as glass, upon whose electron beam confrontingside are deposited the phosphors which constitute the light emissive screen elements. rThese elements are preferably in the form of narrow, closely spaced parallel strips of phosphor materials, adjoining strips being emissive of light of different primary colors,v but any other geometrical contiguration may be used for these screen elements which is appropriate to the pattern traced by the electron beam upon the screen structure and to the order of occurrence yof color representative portions of the received signal.

Upon the beam confronting side ofl these phosphor elements there is next deposited a thin lm of electron permeable conductive material and on this conductive" lilm therej is deposited, in turn a plurality of the aforementioned indexing elements in lizvnown` geometricalrelation- Patented July 24, 1955k ice ship to the pattern of the phosphor elements beneath the conductive film. These indexing elements are characterized in that they are made of a material which responds diiierently tobeam impingement than do those portions of the conductive ilm on which no indexing elements are deposited. If, as is often the case, the conductive film is made of aluminum, which is known to have a comparatively low secondary electron emission ratio, then the indexing elements may appropriately be made of a material having a substantially higher secondary electron emission ratio than aluminum. If there is further provided a suitably energized collector electrode for secondary electrons emitted from the screen structure in response to beam impingement, then a much larger number of secondary electrons will flow from the screen to the collector electrodey during intervals when the electron beam impinges upon indexing elements than during intervals when the beam impinges upon portions of the aluminum layer which are not covered with indexing elements. These Variations in intensity of secondary electron iiow produce corresponding variations inthe current flow through an external circuit connecting the collector electrode to the aluminum lm. The latter current variations constitute the aforementioned indexing signals and can be utilized in any conventional manner. A screen structure of the type generally described hereinbefore, and associated circuitry for uitilizing the indexing signals which it produces to assure beam impingement registry, is disclosed in the copending U. S. patent application of Carlo V. Bocciarelli, Serial No. 198,709, led December l, 1950, and

assigned to the assignee of the present invention.

` toward the interior of the tube.

Alternatively the indexing elements may be formed of light emissive phosphor materials. In that event, impingement of the beam upon an indexing element will causethe emission of light from this element toward the interior ofthe tube, while impingement of the electron beam upon `portions of the aluminum layer on which no indexing elements are deposited will produce no light emission Consequently a photoelectric cell, which views the screen structure from the interior of the cathode ray tube, will be subjected to variations in intensity of illumination as the electron beam traverses alternately indexing elements and bare aluminum portions between indexing elements. In response t0 these light variations the yphotoelectric cell will generate a varying output current which may again be utilized as the indexing signal. It will be noted that, in any case, light is also emitted from the image producing phosphors in response to electron beam inmpingement. However, this light emission takes place on the side of the aluminum filmY which faces away from the photoelectric cell and will be prevented from affecting the photocell by the aluminum iilm which is not transmissive of such light to any substantial degree.

In fact, it will now be recognized that the aluminum iilm acts to separate from eachother, both opticallyand electrically, materials which are deposited on opposite sides thereof, for not only is light incapable of penetrating this film but so are secondary electrons. Consequently, Where secondary electrons are used for indexing, those which are emitted from the phosphor elements of the screen structure in response to beam impingement will be intercepted by the aluminum ilm before they can contaminate the indexing indications produced by secondary electrons emitted from the indexing elements. When light is used for indexing, the aluminum film prevents light from the image productive phosphors from contaminating the indexing indications. This isolation, both. electrical it will be understood that, in its application to a color television cathode ray tube, the aluminum film retains the light intensifying property for which its presence has long been valued in black-and-white television picture tubes.

Whilethe desirability' of the foregoing typeof screen structure has been recognized, it has not been widely adopted because serious difficulties are encountered when its manufacture is attempted While all of the steps involved in the manufacture of such a screen structure are comparatively diflicult, none is more forbidding than the step of forming the indexing elements on top of the aluminum film. The reason for this will be readily understood when it is recalled that the aluminum layer must be extremely thin in order to permit the electron beam to traverse it without prohibitive attenuation. As a matter of fact, it is well known from experience with black-and-white picture tubes that `the thickness of the aluminum film must be limited to about 1000 Angstrom units, or 4 millionths of an inch. The deposition of a comparatively heavy layer of indexing material on such a tenuous film would obvious be a touchy operation evenif the aluminum film itself were firmly supported. In practice, however, no such firm `support exists. This is because the light emissive screen on whichthe aluminum film is formed consists of aggregates of discrete phosphor particles, many of which protrude irregularly from the film confronting surface of the screen. The aluminum film, which must be optically smooth if its potentialities for intensifying the televised image are to be realized, musttherefore be stretched, unsupported, across the gaps between these protrusions. It is to be expected that, in its unsupported regions, a metallic film as thin as the aluminum film in question will have very little mechanical strength. This `expectation was confirmed as soon asyit was attempted to deposit the additional material required for formation of the indexing elements on top of this aluminum film by anyof the orthodox methods which have been used in the past for If the par-l the deposition of various screen materials. ticles additionally deposited werecomparatively large, then their mass was` also relatively great and they would rupture the tenuous aluminumlm at the points where they contacted it. This occurred even though special precautions were taken to deposit the particles as gently as possible. `If, on the other hand, the particle size was decreased to the point where damage from impact be carne less likely, then the particles tended to penetrate the aluminum film through minute, intermolecular apertures therein and to produce swelling of the `organic gel on which the aluminum film is supported during screen structure formation, again causing rupture and blistering of the aluminum. In fact it has been found that, of any given number of screens which were successfully aluminized,` only a very small percentage had a fault free aluminum film after application of the indexing material. This difficulty was particularly troublesome because the faulty portions of the aluminum film were often hidden beneath the indexing elements and were therefore discoverable only after the tubehad been completed and had been tested under actual operating conditions. When a fault was discovered at this late stage of the manufacturingprocess, the entire tube had to be scrapped. As might bewexpected, the combination of the foregoing difficulties increased the unit cost of each successfully produced tube to the point where the entire operation became commercially impractical. The problem was further aggravated by the continuing trend toward tubes with ever larger screens, as it was found that the percentage of tubes with satisfactory aluminum films decreased appreciably each time the size of the screen was increased.

Accordingly it is a primary object of the invention to provide an improved method of manufacturing cathode ray tubes.

It `is another object of the invention to provide an 4 improved method of manufacturing cathode ray tube screen structures.

It is still another object of the invention to provide an improved method of manufacturing cathode ray tube screen structures having a light reflective, electron permeable film of conductive material superposed on the image productive phosphors of the screen and having additional material superposed on said film of conductive material.

It is a still further object of the invention to provide au improved method of manufacturing cathode ray tube screen structures suitable for use in color television picture tubes.

Still another object of the invention is `to provide an improved method of manufacturing a screen structure for a color television picture tube, the screen structure comprising an array of phosphor elements emissive of light of different primary colors disposed in a predetermined geometrical pattern, an electron permeable aluminum film supported by said phosphor elements, and indexing elements supported by said aluminum film and disposed in known geometrical pattern relative to the pattern of the phosphor elements.

A stillfurther object of the invention is to provide an improved composition for use in my improved method of manufacturing cathode ray tube screen structures.

The foregoing objects of the invention, as well `as others which will appear hereinafter, are realized in the following manner. First there is produced, on a suitable substrate by conventional techniques, a phosphor screen of any desired form with a superposed aluminum film or layer for the purposes hereinbefore mentioned. The phosphor screen may be deposited by any of the con ventional procedures hereinbefore mentioned, and an organic film or layer may then be applied to the phosphor screen by conventional procedures to condition it for the subsequent application of an aluminum ilm or layer which likewise is laid down by conventional techniques. As hereinbefore stated, it has not heretofore proved feasible to deposit either secondary emissive or light emissive indexing materials directly on this aluminum layer without grave danger of irreparably damaging either the aluminum layer and/or the underlying phosphor screen. I have discovered, however, that it is feasible to deposit directly on the aluminum layer a layer of suitable organic material which has the effect of protecting the aluminum layer and permitting the subsequent application to it of the desired indexing materials. If desired, after the in dexing materials have been so deposited on the reinforced aluminum film, the entire structure may be dried and baked to eliminate the film of organic material so that the indexing elements will then adhere directly to the aluminum film. While in the past, and as hereinbefore mentioned, it hasbeen customary to apply suchan organic film to a phosphor screen before the application of an aluminum film, it should be noted that the problems there involved are not the same as those which gave rise to the present invention and it would not have been apparent to one skilled in the art that it would be possible to apply an organic film on an aluminum layer which in turn was superimposed on a phosphor screen. Moreover it would not have been apparent to one skilled in the art that the prior application of such an organic film to the aluminum film would make `it possible to apply other materials, such as the indexing materials hereinbefore mentioned, to the Surface of the aluminum film. Indeed it could only reasonably be concluded, from the fact that attempts to deposit indexing materials directly on `the aluminum film were unsuccessful and resulted in damage to the film and to the underlying phosphor screen, that an attempt to apply an organic `film to the aluminum layer would result in similar damage to the aluminum and to the underlying phosphor screen. In fact this was the conclusion reached, prior to the making of the presentinvention, by numerous experts in the iield who had all but abandoned the hope of applying other materials over such an aluminum film. The reasons for this will be appreciated more fully from a consideration of the differences between the` problems presented in the present instance and in the rprior art. These Will be more readily apparent after my-invention has been explained in detail, and accordingly will be discussed more fully hereinafter.

As will be seen from the detailed description of the invention which is to follow, the practice of my invention makes feasible, for the iirst time, the manufacture of cathode ray tube screen structures. of the type under consideration of Virtually any desired size with substantialfreedom from blemishes in the aluminum iilm caused by the application of the indexing material.

The particular method of manufacturing cathode ray tube screen structures in accordance with my invention is explained in detail with' reference to the accompanying drawings, in which:

Figure l is a greatly enlarged fragmentary view of the form of screen structure resulting from the manufacturing process which embodies my invention;

Figure 2 is a iiow chart of the steps which characterizeV the processof my inventive method; and` Figure 3 is a flow chart of an alternative method of manufacturing the screen structures of Figure 1 in accordance with my invention.

The structure of the cathode ray tube screen illustrated in Figure l of the drawings, to Which more particular reference may now be had, is entirely conventional in all respects, consisting of a glass substrate'ltwhich may be either the face plate of the cathode ray tube itself or a separate glass plate supported Within the tube envelope. Upon this glass substrate there are disposed a plurality of vertical phosphor strips, of which thosedesignated 11 are made of a fluorescent material emissive of red light in response to impingement by the electron beam of the cathode ray tube. T hose strips designated 12 are made of a uorescent material responsive to electron beam impingement to emit green light, while thosedesignated 13 are responsive to emit blue light. As is also conventional, the entire surface area of these strips 11, 1-2 and 13 is covered by a lm 14v of a highly light reflective, conductive material such as aluminum and suiiiciently thin to be permeable to the electrons of the cathode ray beam. On the electron beam confronting side of this aluminum iilm 14 there are in turn disposed a plurality of so-called indexing strips 15, which are arranged in a predetermined geometrical relationship With respecty to the phosphor strips 11, 12 and 13 and which are normally characterized by having a secondary electron emission ratio which diifers substantially from that of the aluminum iilm. In practice the indexing strips 15 willV frequently be disposed as shown, namely in alignment with phosphor strips emissive of light of one particular color, green for example. There will theny be an indexing strip superposed upon every third phosphor strip and sepa` rated therefrom by the aluminum film 14. However, it will be understood that this particular arrangement of indexingvstrips is not essential to my inventive concept. Rather, the particular indexing strip arrangement shownr here is purely exemplary and any other configuration of such indexing strips relative to the phosphor screen elements may be obtained by the applicationr of the principles hereinafter set forth. Suitable materials. of which these indexing strips may be made include principally those having an electron emission ratio which is considerably higher than that of the aluminum layer. A variety of materials, such as magnesium oxide, barium oxide, strontium oxide, calcium oxide and magnesium orthosilicate have this property.

One particular mode of practicing the method which constitutes my invention -is illustrated in the flow diagram of Figure 2, .to which more particular reference; may now be had. This method starts with the deposition of the phosphor strips on the glass substrate of Figure.. l.

This. operationis symbolized by. rectangle 16 of Figure fluorescent material -through transparent slit-like portions in an otherwise opaque mask, these transparent port-ions having been formed at positions corresponding .to the desired locations of strips of that particular phosphor. This exposure fixes the phosphor of the exposed portions and Ithe remaining, unexposed phosphor is washed off. This process is repeated successively with each of the other two phosphors, the mask being relocated each .time so as to permit exposure of the proper portions Iof the phosphor which it is desired to have remain on the glass substrate. The aforedescribed process is similar to that described in detail in the copending U. S. patent applicationof John W. Tiley, Serial No. 248,356, iiled September 26, 1951 and assigned to the assignee of thev present invention. A variety of phosphors are known which lend themselves to this Iprocess .of manufacture. Particular phosphors which I have used with success in for-ming the uorescent portions of my screen are zinc phosphate for the red light emissive strips, zinc orthosilicate for the green light emissive strips and calcium magnesium silicate for the blue light Iemissive strips.

The next step iny processing the assembly of glass substrate and phosphor strips consists -in depositing thereon of an yorg-anic iilm to provide astri-table base for the su-bsequent deposition of an aluminum film. This step is symbolized by rectangle i7 of Figure 2. Substances are known which. .are suitable for the formation of such an organic lm. For example .this llm may 'be constituted 'of the materials which are disclosed for this purpose in lthe copending U. S. patent application of Miriam G.

Groner, Serial No. 254,195, led October 31,` 1951 and` assigned to the assignee of the present invention. The organic film disclosed therein comprises a liquid composition constituted of a small amount of nitrocellulose, a 'Water insoluble plasticizer therefor and octyl acetate dissolved in a mixture of a water soluble alcohol and a volatile ester, the volatile ester being the major constituent `of the composition. In particular the alcohol is preferably selected from the group consisting of a propyl alcohol and a butyl alcohol, and the ester is preferably selected from the group consisting of a propyl acetate andy This liquid composition is permitted,

a butyl acetate. to spread over the surface of the previously deposited phosphor strips and'also over the exposed portions of the glass substrate wherever, as shown in Figure l, this glass substrate is not covered by the phosphor strips. This composition is a thin, mobile liquid which readily spreads over -the phosphor strips and forms a iilm containing nitrocellulose, the edges of which adhere to the sides of the cathode ray tube` bulb. As is fully explained in'the aforementioned Groner application, it is an important 'advantage of this composition that the alcohols included the-rein are water soluble and the esters vol-atile. lof this, when the composition is applied to the phosphors which, at this stage, contain an appreciable quantity of lwater left over from theaqueous s-olution in which they are first deposited, the aforementioned constituents of 'the hlm formingcomposition are gradually removed from the `ilm by being leach-ed out by `the aqueous component of lthe phosphor strips in the case of the alcohol, and by being vaporized intothe air above the layer of iilm forming -composition in the case of the volatile esters. This continues until the nitrocellulose containing. layer loses its liquid nature andV becomes a tacky, flexible, extensible solid vtil-m. Theyoctyl 4acetate, being insoluble in the aque?.

Because nitrocellulose film and, along with the plasticizer, imparts thereto the state of tackiness, flexibility and extensibility, When, during the finalrbake out stage of the completed screen structure the aqueous suspending medium is cornpletely removed from the phosphor strips, the nitrocellulose filrn will be caused to sag further and to settle until it rests upon the phosphor strips. The fiexibility and extensibility imparted to,u the film by the octyl acetate in conjunction with the plasticizer permits the film to sag, stretch and otherwise withstand the stresses and distortions involved without breaking. Further drying `then removes the octyl acetate and any residual water soluble alcohol and volatile ester from the film, causing the lm lto `shrink and to `assume a smooth, stretched charac-ter resting on the protruding phosphor particles in the phosphor layer. It will be understood that no invention is predicated on this particular manner of forming the organic film on the phosphor strips, the particular process described being merely illustrative of a preferred mode of accomplishing this step. Other conventional methods of forming this organic lm may be used instead, the only requirement being that an organic film be formed whose electron beam confronting surface is sufficiently smooth to permit the depositi-on of an aluminum film thereon having the desired optical reflecting properties for light which `is emitted from the phosphor strips toward :the interior f the tube. t

The next step of the process, `symbolized in Figure 2 by rectangle 18, is the deposition of such an aluminum film. This may be accomplished in any desired manner, as for example lby evaporation from a thin aluminum filament suspended near the screen structure and heated to its evaporatingrtemperature by the passage of current directly therethrough, or through a supporting element with which it is in heat `exchanging relationship. By control of the evaporation period and of 'the rate at which evaporation takes place during this period, it is possible readily to control the thickness of this aluminum film. As h'as been pointed out it is essential that this thickness be limited to such a value that the aluminum film remains electron permeable, for otherwise the` electron beam will be unable to excite the colored light emissive phosphors. It is apparent that, the thinner this aluminum film is, the greater will be the fraction of the impinging electron beam which is transmitted to the phosphors and the higher will be the intensity of the light which is emitted by these phosphors in response to a beam of a given intensity. Therefore, even within the limits of electron permeability, it is desirable to `make this aluminum film as thin as possible consistently with maintaining its iight reflecting properties. As has been indicated it is currently `feasible to produce aluminum films which are only about four millionths of an inch thick by the aforementioned evaporation process, by sputtering, or by other conventional methods. Indeed it is the very fact that the use of such extremely thin aluminum films is both necessary `and feasible which makes it so difiicult to deposit the additional indexing material on the in'terior surface of the screen structure.

In the formation of the screen structure in accordance with my invention, the next step is symbolically represented by rectangle 19 in Figure 2 and involves the deposition of a second -organic film on the exposed surface of the aluminum film formed in step 1'8. This deposition of an organic film on top `of the aluminum film may be carried out in any desired manner, as for example by spraying or by fiowing the `lacquer onto the aluminum film. In any case, however, care should be taken that as little pressure as possible is applied to `the aluminum film during deposition of the organic film thereon. Ac-` cordingly, when spraying the organic film onto the aluminum film, I have used pressures which exceed atmospheric pressure by as little as one half pound per square inch. While it is possible to use, for the organic film applied in step 19, the same ina-terialas is used for the organic 8 film which is applied prior to the deposition of the aluminum film, il e. in step 17, it is preferred to` use, on top of the aluminum film, -a composition which includes no water` soluble alcohol` but instead includes a higher percentage of plasticizer than the organic film material of step 17. Thereason for omitting the water soluble alcohol is that generally at this stage there will be no water present which is capable of leaching out this alcohol. The increase in the percentage of plasticizer is .prompted by the desire to cause as little stretching as possible of the organic film on top of the aluminum film, as such stretching might cause the aluminum film to lift up from i-ts position in contact with the underlying materials and particularly from its position on the underlying organic` film applied in step 17. This lifting is particularly likely to occur along the outer edges of the screen structure. Naturally such lifting is likely to tear and otherwise damage the aluminum film, thereby destroying the usefulness of the screen structure. The use of additional plasticizer material, as 'hereinbefore suggested, is permissible in the case of the organic film deposited on top of the aluminum film because the indexing strips, which are to be deposited on lthis organic film, need not have the optical reflecting properties of the phosphor confronting surface of the aluminum film, so that it is not necessary to provide the same smooth substrate therefor as is provided for the aluminum film by the contraction of the organic film with low plasticizer content upon which the aluminum film rests. A preferred composition of the organic material applied in step 19 under discussion consists of 5 grams of nitrocellulose, 5 milliliters of a plasticizer whose chemical name is di-Z-ethylbutyrate triethylene glycol and which is sold by the Carbide and Carbon Chemical Company as type 3GH Flexo1, and

`250 milliliters of iso amyl acetate.

The next, and penultimate step of the process of Figure 2, symbolically represented therein by rectangle 20, involves the deposition of the indexing strips. This may be carried out in any conventional manner, as, for example, in the same manner as the deposition of the phosphor strips on the glass substrate. In the event that these phosphor strips are deposited by the photographic process hereinbefo-re outlined, it suffices to deposit the material of which the indexing strips are to be constituted on the organic film formed in step 19 in a suitable photosensitive solution, after which the solution may be exposed to illumination through the same mask which was used for the formation of the phosphor strips, care being taken to reposition this mask so that the transparent portions permit light to fall upon the portions of the screen structure on which indexing strips are to be formed. It should be noted, in this connection, that itis entirely feasible to expose the indexing material which is located on top of the organic film through all of the previously formed portions of the screen structure, and in particular through the aluminum film formed in step 18,1 provided a sufficiently intense source of illumination is used and provided this exposure is continued for a sufficiently long interval. Alternatively it is possible to expose the materials used in the deposition of the phosphor strips of step 16 from the face plate side of the screen structure and to expose the indexing material from :the beam confronting side of the screen structure.` However, this latter method involves serious problems of registry between the mask or masks used for `the selective exposure from opposite sides and it is preferred to carry out all the exposures from .the same side of the screen structure, whether this be the face plate side or the beam confronting side.

The final step of the process, symbolized by rectangle 21 in Figure 2, consists in drying and baking the screen structure formed by the foregoing steps 16 to 20 inclusive. While thedrying operation may be carried out at any time, the bakingis preferably done after the screen structure has been incorporated into the tube envelope and after other conventional components of the cathode ray tube have also been placed therein in their usual locations.

It will now be apparent that the organic film, which is deposited on topof the aluminum film, plays an entirely different role in my screen manufacturingmethod than does the organic film which is deposited beneath the aluminum film. In particular, the organic film beneath the aluminum film is provided for the purpose of forming a smooth surface to which the aluminum film will conform upon deposition, so thatv the aluminum film will acquire the desired optical reflectingproperties. So far as the deposition of the aluminum film itself is concerned, the fragility of the underlying material is clearly no problem, since the glass substrate, as well as the phosphor strips which are formed thereon, are sufiiciently sturdy to support not only the weight of the thin aluminum film but also the weight of structures many times as heavy as this film, such as, for example, the indexing strips deposited on the back of the aluminum film. On Ithe other hand, the second organic film, which is deposited on top of the aluminum film prior to application of the indexing strips, is provided for the purpose of insuring that the subsequent application of the indexing material will cause no damage to the extremely fragile aluminum film beneath. That the organic film is capable of affording such protection, without itself damaging the aluminum fihn, is a fact which previous experience with the use of organic films as the supporting media for the aluminum films had not suggested in any way. On the contrary, prior experience with organic films tended to indicate that comparatively heavy particles, such as those used in the formation of the indexing strips, would readily traverse an organic film and continue to penetrate the aluminum layer beneath, with consequent damage to this aluminum film. As a matter of fact, it was the universal view of those skilled in the art prior to my invention that the thin aluminum film used in cathode ray tube screen structures was quite incapable of supporting any appreciable weight without rupture, so that the application of any substance whatsoever to its beam confronting surface was considered to be impractical.

lt is also considered to be noteworthy that the protection against damage resulting from the application of substances to the aluminum film, which is afforded by the organic film deposited on its beam confronting surface, appears to continue, in some manner which is not as yet clearly understood, even after this organic film has been substantially evaporated by the bake-out operation, for screen structures manufactured in accordance with the process hereinbefore outlined show a greatly reduced tendency toward blemi-shes in the aluminum film even after extended periods of use following deposition of the indexing strips and incorporation of the screen into a completed cathode ray tube structure.

As has been pointed out, the deposition of indexing material on the aluminum film, as it was attempted unsuccessfully in the prior art, damaged the aluminum film either by reason of the direct impact of the particles of the indexing material or because some of this indexing material penetrated the aluminum lm and caused swelling of the underlying film of organic material. When an organic protective film is interposed between the aluminum film andthe indexing material in accordance with my invention, the latter becomes substantially incapable of causing damage in this manner. However, when the organic protective film is made, as it sometimes is, of such ingredients that it has very low viscosity, then small quantities of the most fluid ingredients of this protective film may penetrate through the intermolecular apertures in the aluminum film and may themselves cause sufficient swelling of the underlying supporting film to damage the aluminum film.

Where it is desired for any reason to use a protective organic film of such low viscosity, l have found that it is still possible to practice my invention to good advantage provided certain additional precautions arealso taken. Theprocess which must be used in such asituation is illustrated diagrammatically in the flow chart of Figure 3, to which more particular reference may now be had. It will be apparent by inspection that the process illustrated in Figure 3 is similar to that illustrated in Figure y2 in its essential features. in particular, both processes are characterized by the application of a first organic film directly to colored light emissive phosphors of the screen structure and by the application of a second organic film to the aluminum film prior to the deposition of indexing material on the previously formed portion-s of the screen structure. However, the two processes differ in a number of important particulars. For example, the first step of the process illustrated in Figure 3, which is represented symbolically by rectangle 22, unlike the first step of the process of Figure 2, comprises not only the deposition of phosphor materials alone, but also the deposition of an inorganic binder material which is distributed more or less uniformly in the interstices between the phosphor particles in sufficient quantity to insure cohesion between these particles and adhesion thereof to the gla-ss substrate. The next two steps of the method, respectively symbolized by rectangles 23 and 24 in Figure 3, are similar to the second and third steps (17 and 18)k of Figure 2, consisting as did the latter, of the deposition of an organic film on the phosphors and of the deposition of an aluminum film on this organic film. But whereas, in the process of Figure 2, the second organic film was immediately applied to the aluminum layer, this is not done in the process of Figure 3. Instead, the previously formed portions of the screen structure, including the phosphor strips in their inorganic binder, the organic film and the aluminum film, are now dried and baked until the organic film is substantially completely vaporized. Only after this step, which is symbolically represented by rectangle 25 in Figure 3, is completed, is the second organic film deposited on top of the aluminum film. This last-mentioned step is symbolized by rectangle 26 of Figure 3. Thereafter indexing strips are deposited on the organic film, as symbolized by rectangle 27, and the resultant screen structure is dried and baked, as symbolized by rectangle 28, and is thus brought to completion in the same manner as in the process of Figure 2.

Thus it will be seen that the process of Figure 3 differs from that of Figure 2 principally in the addition of an inorganic binder material to the phosphor strips and in an additional drying and baking operation which is carried out after the deposition of the aluminum film and before the deposition of the second organic film thereon. The purpose of' the additional drying and baking step 25 is to rid the screen structure of the first deposited organic film before the second organic film is applied. Once this has been done, it is clearly immaterial whether or not ingredients of the second inorganic film penetrate the aluminum layer for there is now no organic film present beneath this aluminum layer which could be swelled by this penetrating material. Consequently no damage to the aluminum film can be caused by such penetration. At the same time, however, the cohesive effect of the organic film, which is deposited prior to deposition of the aluminum hlm on the phosphors and which it is preferred to retain until the final bake-out of the tube, is also lost by the intermediate bakeout operation which vaporizes this organic film. The inmorganic binder material, which is not susceptible to vaporization by this bake-out operation, is provided to substitute for the first organic film in this respect. lnorganic binders suitable for this purpose are potassium silicate and sodium silicate, but many others are, of course, also available.

In the foregoing discussion, my novel method has been described in its application to the deposition of secondary electron emissive indexing elements. However, it will be recalled that sometimes photoclectric indexing elements are preferred. It is therefore desired` to emphasize that by the practice of my novel method it is equally feasible` to deposit light emissive phosphors on top of the aluminumy film as it is to deposit secondary electron emissive materials, the essential requirement in either case being the aforementioned prior deposition of the intervening protective film.

lt will be understood that other modifications of the manufacturing methods hereinbefore described in detail will occur to those skilled in the art without departing from my inventive concept. Accordingly I desire to limit the scope of this concept only by the appended claims.

I claim:

l. The method of depositing inorganic material on the surface of a film of metallic conductive material, said film being sufficiently thin to be permeable to the electrons of a cathode ray beam impinging thereon, said method comprising the steps of depositing a film of heat removable, film forming organic material on said conductive film, depositing said inorganic material on said organic film, and heatingr the structure so formed until said organic film is substantially completely ,Vaporized 2. The method of depositing particles of inorganic material on the surface of a metallic film, said metallic film being sufficiently thin to be permeable to the electrons of a cathode ray beam impinged thereon and said metallic film being suspended between spaced protrusions from a substrate, said method comprising the steps of depositing a film of heat removable, film forming organic material on said metallic film, depositing said particles of inorganic material on said organic film, and heating :the structure so formed until said organic film is substantially completely vaporized.

3. The method ot' forming a screen structure for cathode ray tubes on a substrate of solid material, said method comprising the steps of: depositing a layer of phosphor materials on said substrate, depositing a first film of heat rcmovableJilm forming organic material on said phosphor layer, depositing a metallic film on said organic film, said metallic film being sufficiently thin to be permeable to the electrons of a cathode ray beam, depositing a second film of heat removable, film formingorganic material on said metallic film, depositing `on said second organic film a layer of material having a response characteristic to electron impingement which is substantially different from the response characteristic of `said metallic film to electron impingement, and heating the structure so formed until both of said organic films have been substantially completely vaporized.

4. The method of forming a 4screen structure for cathode ray tubes on a substrate of solid transparent material, said method comprising the steps of: depositing a fiuorescent screenon said substrate, depositing a first film of heat removable, film forming organic material on said fluorescent screen, depositing a metallic film on said first organic film, said metallic film being sufficiently thin to be permeable to the electrons of a cathode ray beam, depositing a second film of heat removable, film forming organic material on said' metallic film, depositing on said second organic film material having a response characteristic to electron impingement which is substantially different from the response characteristic of said metallic film to electron impingement, said last-named material being deposited in predetermined geometrical configuration relative to said fiuorescent screen, and heating the structure so formed until both of said organic films have beenzsubstantially completely vaporized.

5. The method of forming a screen structure for cathode ray tubes on a substrate of solid transparent material, said method comprising the steps of: depositing a fiuorescent screen on said substrate, depositing on said fiuorescent screen a film of heat removable, film forming organic material comprising a relatively lowpercentage of plasticizer, depositing a metallic film on said organic film, said metallic film being sufficiently thin to be permeable to the electrons of `a cathode ray beam and sufficiently thick to 12 be substantially non-permeable to light emitted from said fiuorescent screen, depositing on said metallic film a film of heatremovable, film forming organic material comprising a relatively high percentage of plasticizer, depositing on said last-named organic film a layer of material having a response characteristic to electron beam impingement which is substantially different from the response characteristic of said metallic film to electron impinges ment, and heating the structure so formed until both of said organic films have been substantially completely vaporized.

6. The method of claim 5 further characterized in that said organic material constituting said second organic film comprises a sufficiently high percentage of plasticizer so that said second organic film will not contract appreciably during heating.

7. The method of forming a screen structure for cathode ray tubes on a substrate of solid transparent material, said method comprising the steps of: depositing on said substrate a layer of phosphor materials in an inorganic binder, depositing a first film of heat removable, film forming organic material on said phosphor layer, depositing a metallic film on said organic film, said metallic film being sufiiciently thin to be permeable to the electrons of a cathode ray beam, heating the structure so formed until said first organic film is substantially completely vaporized, depositing a second film of heat removable, film forming organic material on said metallic film, depositing on said second organic film a layer of material having a response characteristic to `electron impingement which is substantially different from the response characteristic of said metallic film, and heating the structure so formed until said second organic film is substantially completely vaporized.

8. The method of claim 4 further characterized in that said fiuorescent screen comprises different portions constituted of phosphors emissive of light of different primary colors and disposed in a predetermined geometrical pattern.

9. The method of claim 4 further characterized in that said material deposited on said second organic film has a secondary electron emission ratio substantially greater than that of said metallic film.

l0. The method of claim 9 further characterized in that said material of high secondary electron emission ratio is magnesium oxide.

l1. The method of forming a screen structure for cathode ray tubes on a glass substrate, said method comprising the steps of: depositing a phosphor screen on said substrate, depositing a first film of organic material on said phosphor screen, depositing an aluminum film on said organic film, said aluminum film being suficiently thin to be permeable to the electrons of a cathode ray beam, depositing a second film of organic material on said metallic film, said organic material of said second filni being a composition of nitrocellulose, Water insoluble plasticizer therefor, and octyl acetate dissolved in a volatile ester, depositing on said second organic film a layer of material having a response characteristic to electron impingement `which is substantially different from the response characteristic of said aluminum film to electron impingement, and heating the structure so formed until both of said organic films have been substantially completely vaporized, the percentage of plasticizer in said composition constituting said second organic material being sufficiently high so that no substantial contraction of said second film of organic material takes place during said vaporization of organic films.

12. The method of forming a screen structure for cathode ray tubes on a substrate of solid material, said method comprising the steps of: depositing a layer of phosphor materials on said substrate, depositing a first film of heat removable, film forming organic material on said phosphor layer, depositing a metallic film approximately 1060 Angstrom units thick on said organic film,

depositing a second film of heat removable, film forming organic material on said metallic film, depositing on said second organic film a layer o-. material having a response characteristic to electron irnpingement which is substantially different from the response characteristic of said metallic film to electron impingement, and heating the structure so formed until both of said organic films have been substantially completely vaporized.

13. The method of forming a screen structure for cathode ray tubes on a substrate of solid material, said method comprising the steps of: depositing a layer of phosphor materials on said substrate, depositing a first film of heat removable, film forming organic material on said phosphor layer, depositing a metallic film on said organic film, said metallic film being sufiiciently thin to be permeable to the electrons of a cathode ray beam, depositing a second film of heat removable, film forming organic material on said metallic film, spraying onto said second organic film particles of a material having a response characteristic to electron impingement which is substantially different from the response characteristic of said metallic film to electron impingement, and heating the structure so formed until both of said organic films have been substantially completely vaporized.

14 14. The method of claim 13 further characterized in that said spraying of material onto said second organic film is carried out under pressure which exceeds atmospheric pressure by approximately one-half pound per square inch.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Chicago Club, Gfficial Digest of the Federation of Paint and Varnish Production Clubs (1945), pp. 493-503. f 

1. THE METHOD OF DEPOSITING INORGANIC MATERIAL ON THE SURFACE OF A FILM OF METALLIC CONDUCTIVE MATERIAL, SAID FILM BEING SUFFICIENTLY THIN TO BE PERMEABLE TO THE ELECTRONS OF A CATHODE RAY BEAM IMPINGING THEREON, SAID METHOD COMPRISING THE STEPS OF DEPOSITING A FILM OF HEAT REMOVABLE, FILM FORMING ORGANIC MATERIAL ON SAID CONDUCTIVE FILM, DEPOSITING SAID INORGANIC MATERIAL ON SAID ORGANIC FILM, AND HEATING THE STRUCTURE SO FORMED UNTIL SAID ORGANIC FILM IS SUBSTANTIALLY COMPLETELY VAPORIZED. 